Apparatus for the manufacture of centrifugally cast tubular metal articles



Aug. 16, 1960 F. H. COUPLAND JR., ETA 2,948,934

. Us FOR THE MANUFACT APPARAT iJRE OF CENT UGALLY CAST TUBULAR METALARTICLES Original Filed Feb. 23, 1951 2 Sheets-Sheet 1 AVIIAWIAQIA,

INVENTORS Q Dank co zanm n EduJl'rL H. Phelpm John/M. Crazford KennefihB. DazueL Aug. 16, 1960 F. H. COUPLAND. JR.. ETAL 2, 4

APPARATUS FOR THE MANUFACTURE OF CENTRIFUGALLY gAST TUBULAR METALARTICLES 1 s1 2 SheetsSheet 2 Original Filed Feb I NVENTY )RS Han/c H.cou Edwin, H. P/zeqw' Jolvz M Cram/ 0rd W Wavy). CW2! ATTORNEYS UnitedStates Patent APPARATUS FOR THE MANUFACTURE OF CEN- TRIFUGALLY CASTTUBULAR METAL AR- TICLES Original application Feb. 23, 1951, Ser. No.212,468. Divided and this application Apr. 15, 1953, Ser. No.

6 Claims. 01. 22-1135 This invention relates to the manufacture ofcentrifugally cast tubular metal articles, and is particularly concernedwith an improved apparatus for centrifugally casting iron and steelpipe, tubing and similar hollow bodies of generally cylindrical form bythe method disclosed and claimed in application Serial No. 212,468,filed February 23, 1951, now abandoned, of which the present applicationis a division.

Inasmuch as the invention is especially well adapted to the productionof cast iron pipe, the following disclosure will be directed primarilyto this particular application of the inventive concept. By so doing,however, it is not intended to limit the scope of the invention to thecentrifugal casting of cast iron pipe, because it will be obvious thatit has equal utility in the manufacture of other types of hollow metalcastings.

Heretofore, there have been in general use in the industry only twodifferent methods of centrifugally casting cast iron pipe; the Sandspunmethod employing a sand mold formed by ramming green sand around apattern inside a metal flask, and the de Lavaud process in which a metalmold is used.

In the Sandspun procedure, the sand mold must-be made relatively thick,two inches being a representative thickness, in order to facilitateramming and also prevent the molten metal from being forced out throughthe vent holes which are provided in the metal flask to permit readyescape of the water vapor and other gases formed during the castingoperation. The use of sand molds requires an extensive amount ofmechanical equipment for storing, supplying and reconditioning the sand,ramming the sand into the flasks, maintaining the flask and patterns inproperly centered positions, and cutting out the sand before strippingthe cast pipes from the molds. Considerable labor is also expended inperforming the various manual operations necessary in ramming andstripping the molds. These disadvantages of the sand mold process areoffset to a substantial extent by the fact that the resulting castingshave the desirable characteristics of a typical sand cast gray ironstructure and do not require annealing.

In the de Lavaud method the metal mold is normally water-cooled toreduce the mold temperature produced by the rapid transfer of heat fromthe molten iron, although in some instances air cooling is adequate, andit is usually attempted to protect the mold during casting by the use ofa relatively thin coating or facing of suitable composition, such as drypowdered ferro-silicon or a water suspension of such refractorymaterials as silica flour and bentonite. In most cases, however, suchmold coatings do not retard -the freezing rate sufficiently to preventchilling of the iron, and a subsequent annealing treatment is necessaryto reduce the hardness and brittleness of the as-cast product. In metalmold casting, it .is normally impossible to vent the mold because theliquid iron would flow out through the vent holes, or plug them up,during the casting operation. Consequently, it is one of the limitationsof the de Lavaud process that the mold facing used may not containgas-forming materials, because the only available path for escape of thegases is through the freezing metal with the resultant danger of formingblowholes and leaks in the casting. The difiiculty of providing anadequate protective coating on a non-vented metal mold without causingtrouble due to gas formation in the coating also accounts for theexcessively high maintenance and replacement costs which are incurred inthe use of metal molds. 'Compared with the sand mold process, theprincipal advantages of the metal mold procedure reside in therelatively higher rate of production per casting machine which resultsfrom the rapid rate of solidification of the poured metal, and the factthat it is not necessary to form a new mold for each casting.

The apparatus of the present invention is especially adapted for use ina process which successfully combines the advantages and eliminates thedisadvantages of the previously known rotary sand mold and metal moldprocedures by providing a novel method of forming and using sand lined,vented metal molds to produce high quality unchilled castings rapidlyand efliciently, at low cost and with substantially less capitalinvestment than is required for other centrifugal installations.

The improved mold employed in the new method comprises a noyellyconstructed, vented metal mold and a smooth, uniformly hard, bondedrefractory lining of selfsustaining character which is rapidly andaccurately formed by a carefully controlled centrifugal procedure, andwhich, while of substantially less thickness than the sand molds oftheprior art, is effective both to avoid un duly rapid freezing of thecasting metal and to protect the metal mold against overheating andwear. The mold lining is composed of a mixture of silica sand or othergranular refractory and a dry thermosetting resin which, when heated toa predetermined temperature, forms a homogeneous, strongly bondedrefnactory capable of adhering tenaciously to the metal mold. Once thesand resin mixture has fused and set, it constitutes a smooth, densecoating on the interior of the mold which will readily withstand thewashing action of the molten metal during casting, but, after thecasting has frozen, will disintegrate as a result of burning of theresin under the heat of the solidified metal so as to permit rapid, easystripping of the casting from the mold. Lined molds of this charactermay be prepared in quantity with the use of relatively little sand, and,being non-hydroscopic, may be held in storage for indefinite periods oftime before being used for casting.

The principal object of this invention is to provide a sand lined metalmold of novel character for making centrifugally cast metal pipe andsimilar articles by an improved process which produces clean, smoothcastings having generally the same properties as those obtainable by theSandspun method, but does so more quickly, at lower cost and withsubstantially less equipment and labor than the prior procedure.

Other objects, including the provision of a novel form of vented metalmold, will appear more fully upon consideration of the detaileddescription of the invention which follows. In this connection, it is tobe expressly understood that the specific mold lining and pipe castingprocedure hereinafter described and the particular apparatus shown inthe accompanying drawing are illustrative only and are not to beconstrued as representing the full scope of the invention defined in theappended claims.

In the drawings, wherein like reference characters indicate like partsthroughout the several views:

Fig. 1 is a side View, partially in section, of one form of moldconstructed in accordance with the invention,

3 this view also showing the trough by which the san resin mixture maybe introduced into the metal mold in the position occupied thereby justbefore the mixture is dumped into the rotating mold;

Fig. 2 is an enlarged cross section of the metal mold and trough. takensubstantially on line 22 in Fig. 1;

Fig. 3 is a cross section similar to Fig. 2, but showing the trough ininverted position;

Fig. 4 is a partially sectioned side view similar to Fig. 1 showing thesand lined mold as it exists just prior to pouring of the molten metal;

Fig. 5 is an enlarged half axial section of the bell end of the metalmold of Fig. 1 showing the removable metal insert for shaping the outersurface of the bell of the pipe and the means by which said insert isdetachably fixed in place;

Fig. 6 is an axial sectional view, on an enlarged scale, of the novelform of vent embodied in the metal mold of Figs. 1 and 4; and

Fig. 7 is a view similar to Fig. 6 showing a modified form of vent.

The method of making a cast iron pipe by use of the apparatus of thepresent invention comprises a series of coordinated steps performed atsuccessive stations of aproduction line system adapted for continuous,closed cycle operation.

In practice, the beginning of the cycle may be taken to be thecentrifugal casting step wherein a charge of molten iron is poured intoa rotating mold comprising a vented metal mold having a resin bondedsand lining and rotation of the mold is continued until the cast metalsolidifies or freezes into the form provided byv the mold; During thecasting, the mold is supported in a substantially horizontal positionon, and is rotated by, the motor driven rollers of an ordinarycentrifugal casting machine, and the molten iron is delivered into themold from a tiltable ladle by a relatively short pouring trough of"conventional construction. In making extra long or extra heavy pipe, itmay be desirable to use a longer trough extending a substantial distanceinto the mold andto withdraw the trough as the metal is poured tofacilitate longitudinal distribution of the charge. While the metal maybe poured from either end of the mold, or even simultaneously from bothends, it is preferable to introduce it from hte spigot end when the pipeis to have a bell or flange so that the colder metal will flow into theheavier sections and the hotter metalwill form the thinner sections ofthe casting.

If desired or necessitated by the size and weight of the mold, the moldmay be rotated at a uniform speed throughout the casting operation,which speed must be sufficient to form the casting on the mold wallcentrifugally as the metal is introduced. This is known as high speedcasting and involves a relatively high speed of rotation such as tocreate centrifugal forces at the inner surfiace of the mold on the orderof 60.g to 75 g, Where g represents the force of gravity. For example,in-making a 20" pipe by the high speedicastin-g procedure, it isdesirable to rotate the mold at from 450 to 500 rpm.

It is preferable, however, to introduce the molten iron into the moldwhile the latter is rotating at aspeed below that at which the metal iscaused to cover the mold wall by centrifugal force, so that the metalmay first distribute itself longitudinally in the form of a trough orslab on the bottom of the slowly spinning mold. Then, as soon as all orthe major portion of the charge is in the mold, the rotation isaccelerated to a speed at which the metal will distribute itselfcircumferentially and form the pipe under centrifugal action. Thisprocedure is called low speed casting, and is particularly desirablebecause any loose particles of the mold lining or impurities in themolten metal, together with the slag, will float on top ofthe slab lyingalong the bottom of the mold and will not be trapped against the mo d inwithin the wall of the casting.

mately 75% of the molten iron charge is being poured.

In utilizing the low speed casting technique which is particularlyadaptable to the molds provided by the present invention because theyare substantially lighter than the sand molds used in the Sandspunprocess for making pipe of the same diameter, the mold is spun at arelatively low speed of from 50 to rpm. while approxiintothe mold, andisthen very rapidly accelerated; within a period of from 5 to 10seconds, to a relatively high speed on. the order of ten or more timesthe low speed... For example, in casting a 6" pipe, the mold may berotated at approximately 50 r.p-.m. for about 12, seconds after pouring.of the metal begins, during which time 75% of the metal in the ladle isdelivered into the mold. The speed is then increased in about 6 secondsto ap proximatelySSO r.p.m., equivalent to about 60 g, and'the the highspeed rotation iscontinued until the casting sol fies, which takes onlyabout one minute. Due to the fact that the resin bonded sand liningsofthe molds of the present invention are very much thinner than the sandmolds of the prior art, the length of time required for the casting stepis substantially less than in the Sandspun process, the saving in timebeing between two and. three minutes per cast with a consequent increasein production rate.

Since the temperature of the molten iron is in the neighborhood of 2400to 2500" F. when it is poured and comes into contact with the moldlining, the heat.

of the metal quickly burns out the resin in the lining, thus destroyingthe bond between the. granules of sand and the adhesion of the sand tothe metal wall of the mold. The result is that, by the time the mold hasbeen.

transferred from the casting station to the stripping station, thelining is devoid of strength and the pipe is ready to be strippedwithout any further. operation on. the lining.

At the stripping station, the casting is removed from; the; mold,carryingwith it most of the lining intheform.

mold by the castmetal because, upon completionof the. strippingoperation, the empty mold is returned to the. lining. station where itis prepared for the next cast, atwhichtime it is essential that thetemperature of the mold wall be within a predetermined range such thatthe. heat therefrom will-be sufficient to fuse the new lining;

into a strongly bonded-mass, but not so high as tochar any of the resinin the lining. Accordingly, it is preferable .to strip themold within-aminute or two after the. casting hasfrozen, and toso time the .return ofthe. emptymoldto the lining station that normal atmospheric.

cooling during the return Will reduce the moldtempera ture to withingtherange from300 to 600 F., and-preferably. to between 400 and 500 'F.,the-permissible:

limits of said temperature being dependent-upon the kind and amount ofresin binder used in the lining; If neces-' sary, artificial cooling maybe resorted-to inorderto reduce1themold temperature towithin thedesiredrange between the stripping and lining stations.

If, for any reason, the metal mold is cold when ready to be lined, oritstemperature is below the desired minimum, it may be heated in anysuitable manner, as by gas torches or ina-heating chamber. In-normalopera tion of th'e method, however, each mold'is lined'while thezmetalWall stillretains sufficient heat 'from the previous casting step toexert the desired meltingand polymerizing effect on the-resin ofthelinin'g mixture.

At the lining-station, the metal mold is" provided If desired, theburned.

with a relatively smooth, hard, self-sustaining coating ad-' herent tothe mold wall composed of a mixture of silica sand, or other granularrefractory, and a thermosetting resin, the two ingredients beingthoroughly mixed together in proportions of from 95.0 to 98.5% by weightof sand and from 1.5 to 5.0% by weight of resin. While various types ofresin binders may be used, a two-stage phenol formaldehyde resincontaining approximately of hexamethylenetetramine has been found quitesatisfactory and is preferred because it melts and polymer-izes whenheated to any temperature between 300 and 600 F., a range within whichthe temperature of the metal mold may be readily maintained duringrepeated casting cycles.

The term two-stage phenol formaldehyde resin refers to a resin which isproduced by first reacting to a controlled degree phenol and a limitedamount of formaldehyde, and then incorporating additional formaldehydein the resin in the form of hexamethylenetetramine which decomposes onheating to formaldehyde and ammonia. The characteristics of such a resinare its dry powder form, insolubility in water, fusibility above 300 F.,and capability after melting of polymerizing to an infusible phase withstrong bonding properties. Among the commercially available resins ofthis type suitable for use in the method of the present invention areThor 278, manufactured by the Borden Chemical Company, and R-136,manufactured by the Barret Company. This particular type of resin hasthe further advantage that it undergoes a distinctive color change as itpolymerizes which provides a visual indication of when the lining hasset. A phenol furfural resin containing hexamethylenetetramine has alsobeen used, but is not as satisfactory as the phenol formaldehyde type inthat it does not exhibit the color change above mentioned.

The sand used for the lining should be a good quality, washed silicasand which has been thoroughly dried and then screened to eliminate allforeign matterand provide a sand of the grain size and distributionnecessary to produce the desired smooth mold finish. Sand having an AFSgrain fineness of from 40 to 150 is preferred for the making of castiron pipe, a typical sand having an AFS grain fineness of 100 with 70%on screens. 70 through 200. When casting steel, coarser sand may be usedin order to facilitate escape of the greater amount of gas which isgenerated with the higher casting temperatures of steel. It has alsobeen found that, within the permissible range of grain sizes, thecoarser the sand, the rougher the surface of the lining, but the moreuniform its thickness. Relatively fine sand, on the other hand, providesa smoother lining, but is apt to result in a wavy surface with aconsequent non-uniform thickness.

In preparing the lining mixture, carefully weighed quantities of thedry, screened sand and the bonding resin in dry powder form are chargedinto a suitable mixer or muller in the proportions above indicated,97.0% sand and 3.0% resin being preferred, and throughly mixed together,after which the mixture is transferred to a storage bin from whichmeasured quantities are dispensed as the molds are lined.

The metal molds used in producing pipe in accordance with the presentinvention are generally similar in construction to the mold flasksheretofore used in the Sand-' to be produced, the outer surface of themold being provided with spinning bands or tires for rotating the moldon the motor driven rollers of the lining and casting machines. One endof the mold may be equipped with a hell shape for casting pipes completewith bells orflanges,

the other end being adapted to receive a stop-off plate or core toprevent the molten metal from running out during casting. The insidesurface of the mold which forms the outside contour of the casting mayhave any shape which will allow the solidified casting to be withdrawnfrom one end of the mold, or a split mold may be used for producingother contours. The metal mold is preferably vented in order to permitthe escape of the gases generated in the lining during casting,particularly when making steel pipe or relatively long pipe of othermetals, although vents may not be essential if the mold is relativelyshort.

In forming the mold lining, the empty metal mold, still hot from thepreceding casting or having been other- Wise heated to the desiredtemperature, and with either one or two annular lining stop-off platesattached to its ends, is placed on the rollers of a suitable spinningmechanism, similar to the conventional centrifugal casting machine, andis rotated at a relatively slow speed while a measured quantity of theloose, dry sand-resin mixture is introduced into the interior of themold and distributed uniformly along the axis thereof. If desired, theinside surface of the metal mold may be blacked or coated,

with carbon with an acetylene flame prior to the lining operation. Whenthis is done, there is less tendency for the sand of the lining toadhere to the mold Wall when the cast-ing is stripped from the mold, andwhatever sand may remain in the mold after stripping can be readilybrushed, blown or poured therefrom.

Although the sand resin mixture maybe delivered into the mold in variousways, as by spraying it with air through a nozzle which is passedthrough the mold or by means of an auger conveyor similar to that usedfor the cement lining of pipes, the preferred method is to place therequired volume of mixture to produce a given thickness of lining in atrough of substantially the same length as the mold, evenly distributingthe mixture over the full length of the trough, insert the trough in theslowly rotating mold, and then quickly invert the trough so as to allowthe lining mixture to drop out on the lower portion of the insidesurface of the mold wall. Immediately after dumping the mixture, thetrough is quickly withdrawn from the mold so as to prevent it fromabsorbing heat which might adversely affect the next lining charge. Itis important that, when the trough is inverted to deliver the liningmixture into the mold, the rotation of the mold be slow enough that theparticles of the mitxure are not held to the mold wall by centrifugalforce, but are allowed to roll along the bottom of the inner surface ofsaid Wall. This slow rotation of the mold is continued until the grainsof sand begin to adhere to the wall as the heat therefrom affects thethermosetting resin binder, i.e., for a period of from 2 to 10 secondsafter the trough is dumped.

A-fter continuous adherence is established, rotation of the mold isquickly accelerated to a relatively high speed sufficient to hold theremaining loose granules of the mix ture firmly to the mold wall bycentrifugal force and thereby distribute and tightly pack the mixtureuniformly over the inner surface of the mold. The high speed rotation iscontinued until substantially all of the resin has polymerized andbonded the sand particles together to form a relatively smooth, hardrefractory lining adherent to the mold wall, which result is attained infrom 15 to 30 seconds of high speed rotation, depending upon thethickness of the lining and the flask temperature. When the preferredphenol formaldehyde resin is used, ouring or setting of the lining isclearly indicated. by its change in color from near-white tolemon-yellow or light tan. Should the lining be darker than the desiredcolor, it would indicate that the temperature of the metal mold is abovethe proper range and that some of the resin in the lining is apt to charand thereby weaken the lining if the mold is permited to stand for anysubstantial length of time before being used for casting...

It: has been discovered by experimentation that the proper spinningspeeds of the mold during the lining operation are best determined bythe centrifugal force created at the inner surface of the mold wall andby expressing said force in terms of g, the force of gravity, inaccordance with the formula where N is the speed of rotation of the moldin revolutions per minute and D is the inside diameter of the metal moldin inches. In order to obtain the desired results, the initial spinningspeed to be maintained While the lining mixture is being poured into themold, and until the particles thereof begin to adhere to the mold wall,should be such as to create a centrifugal force not greater than 0.5 g,and preferably on the order of .1 g. After the particles begin to adhereto the surface of the mold wall, the speed of rotation should beaccelerated so as to produce a force not less than 5.0 g, and preferably8.0 g. or higher. For example, with a metal mold having an insidediameter of 7", the lining mixture should be introduced while the moldis spinning at about r.p.m., giving a value of 0.12 g according to theabove formula, and after partial adherence is established, the spinningspeed should be accelerated to about 300 r.p.'m., which is equivalent to9.0 g. While the required spinning speeds will vary with molds ofdifferent diameters, the g factors are maintained substantially constantfor all size molds.

The advantages of forming the mold lining while thus controlling thespeed-of rotation of the mold are several. For example, if the liningmixture is introduced while the mold is rotating more rapidly thanpermitted by the above limitations, the lining will tend to be rippledand uneven, while if the rotation is too slow in the second stage whenthe resin is setting, the coating will lack density and be relativelysoft. By proceeding in accordance with the method described, a smooth,hard, dense coating of any desired'thickness, within the limitshereinafter stated, can be produced.

Another advantage of this lining method is that it permits the use of avented metal mold in spite of the fact that the lining is centrifugallyformed. If a vented mold is-spun too rapidly when the lining mixture isfirst in- -tr'oduced, the particles thereof will tend to be forced outthrough the vent holes, resulting in an uneven and nonuniform lining,with a very thin or nonexistent coating over each vent hole. Byemploying the two speed rotational procedure, small quantities of thelining mixture are permitted to enter andharden in the innermostportions of the vent holes during the initial low speed rotation andthereby effectively seal them against expulsion of sand or resin at thesubsequently higher spinning speed. The lining so produced is, however,quite permeable to gas, particularly as the resin burns out during thecasting operation, so that the vent holes adequately serve theirintended purpose. For example, it-has been found that vents having Ma"diameter openings into the interior of the metal mold, spaced from 3" to8 apart, can be eifectively closed and sealed with a permeablerefractory coating by the present method.

-While the thickness of the mold lining may be varied somewhat toproduce pipes of different diameters in the same metal mold, it has beenfound preferable in practice tocarefully control the lining thicknessfor best repetitive production. The factors governing the thick ness ofthemold lining have already been indicated in functional terms in thegeneral description of the invention'. Although diameter, metal castingtemperature, and other considerations may affect the required liningthicknessto some extent, the principal factor determining the optimumvalue of saidth ickness is the thickness of the metal casting-to beproduced. For example, it has been determined experimentally thatforcastings having a wall thickness from A" to /2 a'- mold liningthiclene'ssof from 0.07 to 0.11" meets the requirements mosteffectively. For thicker castings, thicker linings are desirable.-

ness of the casting. Typical values obtained from this formula are asfollows:

Casting Lining Thickness Thickness Inches Inches 0. 0. 055 O. 25 O, 075;0. 50 0. 106 1. 00 O. 2. 00 0. 212

After the mold has been lined" in the manner above described and thelining stop-off plates have been re moved, the lining is preferablyprovided with a wet fac-- ing which closes the spaces between the sandgrains and" gives a smoother finish to the casting. When the metal to becast is cast iron, the facing or blacking consists of a water suspensionof ground coke andclay; when'-cas'ting steel, a slurry of silica flourand bentonite is pre ferred. Although the facing may be applied in anysuitable manner, as by pouring, spraying or brushing it onto" the innersurface of the mold lining, the preferred procedure involves pouring thefacing into the mold througha funnel while the mold is rotated at arelatively slow speed, withdrawing the funnel and then passing a brushthrough themold while the latter is rotated at a su'bstaii tially higherspeed so as to uniformly distributethe fac'-' ing over the liningsurface. The facing operation may conveniently be performed at thelining station using the same mold spinning mechanism as that employedfor the lining step. The facing'dries relatively quickly'a'fter it hasbeen applied, due to the heat'of'the 'mold wall, andburns out when themolten metal-is poured during'the subsequent casting step.

' prevent chilling of the end of the casting. The m-old'is now ready torepeat the cycle beginning'with the casting step previously described,and may therefore be transferred directly to the casting station. On theother hand, since the facedlining has no afiinity forwater, the linedmold of the present invention can be prepared far in advance of castingand kept for an indefinite period of time before use, if so desired. v

As previously mentioned, the'metal molds employed in practicing the newmethod embody certain features of novelty in comparison with thosepreviously known. One form of moldembo dying the improvements of theinvention has therefore been shown in Figs. 1-6 of theaccompanyingdrawings, which figures also illustrate the mold lining operation andthe characteristics of the mold as it exists when ready for the castingstep.

Referring first to Fig. -1, which shows the metal mold" before the resinbonded sand'lining has-been formed, it will be seen that the mold ismade up of three main parts, an elongated b'ody or center section 61-ofsub stantially cylindrical "form (the greater portion of'wh ichha'sibeen'-=broken away'in F-ig; 1), a belhend'sectfon fii 9 which isthreaded onto and body 61, and a spigot end section 63 similarlythreaded and welded to the opposite end of the body.

The body section 61, which is preferably formed of 64, an enlarged guideflange 66 which cooperates with a' guide rail in known manner toproperly position the mold in an axial direction with respect to therollers of the rotating mechanisms at the lining and casting stations.If desired, one of the spinning bands may be grooved to receive therollers of the rotating mechanisms and so located as to cooperate withthe guide rail, in which event the guide flange 66 may beomitted.

The bell end section 62 of the mold, which is preferably made of caststeel, has an inner cylindrical portion 67 which forms a prolongation ofthe body section 611 and an outer hopper portion 68 of outwardly flared,substantially frusto-conical form adapted to house a removable insert 69for shaping the outer surface of the bell or flange end of the pipe tobe cast in the mold. The insert 69 of the present invention is ofrelatively permanent character, being made of metal, either cast iron orsteel, and is detachably held in place within the hopper 68 by novelmeans which insure accurate centering of the insert with respect to therest of the mold andtight engagement between the inner end thereof andthe abutting end of the inner cylindrical portion 67 of the bell endsection 62.

As shown best in Fig. 5, the outer peripheral surface of the metalinsert 69 conforms to the inner surface of the hopper portion 68 of themetal mold and has formed therein a plurality of radially extendingrecesses 70 equally spaced circumferentially of the insert, the outerportions of which recesses are cylindrical while the inner or bottomportions thereof are substantially conical, as indicated at 71. Each ofrecesses 70 is adapted to receive the similarly conical inner end 72 ofa radially extending cap screw 73 which is threaded through the wall ofthe hopper 68. Inasmuch as the cylindrical and conical portions of eachrecess 70 are of greater diameter and depth, respectively, than the bodyand conical end of the cooperating screw 73, and the conical portion ofthe recess and the conical end of the screw are of the same angularity,it will be apparent that, as the screws are threaded inwardly and theirconical ends 72 engage end of the insert and the abutting end ofcylindrical portion 67 of bell end section 62, as indicated at 74.

The inner circumferential surface of insert 69 mayhave any desiredshape, depending upon the form which it is desired to impart to thecorresponding end of the cast pipe, but is such that, when the insert isin place, said surface forms a smooth continuation of the innercylindrical surface of portion 67 of hell end section 62 which in turnconstitutes a prolongation of mold body section 61. In practice, eachinsert 69 is interchangeable with a number of others having diiferentinside contours. Since the mold lining method previously describedresults in a smooth, dense refractory lining over the entire interiorsurface of the mold, including the welded to one end of the insert 69,the joint between the-inner end of the latter and the mold body iseffectively covered by the lining and leaves no mark on the outsidesurface of the casting.

The outer end of hopper portion 68 of the mold is provided with asubstantially cylindrical rim '75 wherein are formed a plurality ofcircumferentially spaced, radially extending holes '76 adapted toreceive wedge-shaped keys 77 which are driven into said holes from theinside of the rim so that, when the mold is rotated, centrifugal forcetends to force the keys even tighter into the holes. The keys 77 engageand hold in place against the outer end of insert 69 either the annularlining stop-off plate 37 shown in Fig. 1 when the latter is used duringthe lining operation, or the bell socket core 45 shown in Fig. 4 whichis used during the casting step.

Although the present invention is particularly concerned with the use ofinterchangeable, permanent metallic inserts 69 and the obviousadvantages resulting therefrom, it will be apparent that ordinary sandinsert cores might be used instead, if desired, in which case the capscrews 73 could be eliminated and the sand cores held in place by thewedge keys 77.

' The spigot end section 63 of the metal mold is also preferably made ofcast steel and consists of a substantially cylindrical prolongation ofcenter section 61 having at its outer end a radially extending flange 78forming a convenient means for detachable connection to the mold of thelining stop-01f plate 36 of Fig. 1 and the casting stop-off plate 46shown in Fig. 4. In each case, the stop-off plate is provided with aplurality of axially extending stud bolts 79 adapted to pass throughholes in the flange 78 and receive nuts 80 which secure the plate tosaid flange. While the inner surface of lining stop-01f plate 36 issmooth so as to form a square edge at the end of the mold lining, thecorresponding surface of casting stop-off plate 46 is provided with anannular groove 81 which faces the spigot end of the pipe to be cast inthe mold (indicated in broken lines in Fig. 4) and is filled with aquantity of resin bonded sand of the same composition as the mold liningwhich serves to prevent chill-' ing of the end of the casting. It isalso preferable to face the bonded refractory filling of groove 81 withthe same blacking as that applied to the mold lining.

Instead of dividing the metal mold into three sections as shown, it isobvious that the cylindrical portions 61, 63 and 67 may be made in onepiece with a separately formed hopper portion 68 threaded and weldedthereto, or, alternatively, that the entire mold may be machined from asingle casting.

The apparatus for preparing and delivering into the rotating mold thesand-resin mixture for forming the mold lining includes a movable liningtrough 29 which, as indicated in Figs. 1, 2 and 3, may be substantiallyU-shaped in cross section and provided with vertical division plates 30and 31 defining the ends of the portion of thetrough into which ameasured quantity of mixture may bedelivered from a hopper (not shown)which is so designed as to hold the desired amount of mixture necessaryto produce a lining of given thickness. Any suitable means, such as astrike or a leveling vibrator, may be used for evenly distributing thesand-resin mixture throughout the length of the trough.

The trough 29 is so mounted that it can be moved quickly into and out ofthe mold 114 as the latter is rotated, on the rollers of the liningstation, for which purpose the trough may be slidably supported insuitable fixed guides or mounted on a movable carriage running on rails(not shown). If desired, a trunnion 34 may be provided at the end of thelining machine opposite the carirage for receiving a cylindricalextension 35 on the end of the trough 29 (see Fig. 1) so as to ensurethat the trough is properly supported and centered axially with respectto the mold. The mounting of the trough, whether it be in fixed guidesor on a carriage, is such that,

. after the trough has been inserted in the spinning mold, it-

meet

11 ma be quickly inverted as indicated in Fig. 3 to the sand-resinmixture onto the bottom portion of the mold wall and then rotated backto its original position and rapidly'withdr'awn from the mold before thelatter is accelerated for the high speed portion of the liningoperation.

Iirpursuan'ce of the advantages resulting from the use of vented molds,an improved form of vent has been de vised which is particularlyefiective with the mold lining procedure described above. As indicatedin Figs; l-4; the metal mold is provided with a relatively large numberof uniquely constructed vents, indi'cated generally at 82', constitutingopenings through the mold wall for escape of the gases formed duringcasting. The vents 82 are distributed moreor less uniformly over" theentirelength of the mold, with the exception of the hopper portion 68and the spinning band portions 64 and 65. The number and'positioning ofthe vents should be such as to permit ready escape therethrough ofsubstantially all of the gas generated during the casting operation, andwill depend upon a number of factors such as the thickness of thelining, the percentage of resin binder therein; the grain size of thelining sand, the character and thickness or the facing on the lining,and the temperature of the metal being cast. As an example, it has beenfound that, in a mold for casting a 6 cast iron pipe 20 feet long, fouraxially extending rows of vents located 90 apart with a spacing ofapproximately 3.7" between adja'cent vents in the same row, the vents inadjacent rows bein'gstaggered, Will'be adequate under all normal condition's'of lining thickness, amount of resin binder, etc.

As shown best in the enlarged view of Fig. 6, each vent 82 consists of aradially extending hole drilled through the'mold wall having an outerportion '83 of uni-' form diameter which extends inwardly from the outersurface of the mold almost to the inner surface thereof, and arelativelyshort inner portion 84 of substantially smaller diameter which opensinto the interior of the' mold, the shoulder 85 connecting the outer andinner portions of the hole preferably being inclined as shown, ratherthansquare. While the length of the outer portion 83 will-vary with thethickness of the mold'wall, it is desirable tolimit both the length andthe diameter of the innenportion 84-to approximately /3", and to makethe diameter'of the outer portion 83 approximately three times'th'at ofthe inner portion.

When a metal mold having vents of this character is lined according tothe previously described method, the

inner portions 84 of the vent holes become filled with thesand-r'esinlini-ng mixture during the relatively short p'eriodof'slow rotation ofthe mold following dumping of thje'lining trough 29'. Since therelatively small amount of sand-resin mixture ineach of said innervent'portions is'surroun'ded by the heated metal of the mold w'all, thusproviding a relatively high ratio of heating surface to volume-ofthemixture, theresin in each of these quantities melts andpolymerizes very quickly and rapidly fuses the sand' grains together ina rigid, gas permeable mass,

and also 'cements'said mass to the surrounding wall of' the innerportion -84 of the vent hole, before rotation of the" mold isa'cceleratedto high speed and the lining indicated at 86 in Fig.6-isformed. After thisprelim'in'arv closure of the'vent' holes, the-moldlining 861forms in uniform manner over the'entire interior" of the moldand provides an additional coating over the inner ends of the vents ofthe same thickness and density as the rest of the lining:

In some cases, particularly "when relatively fine sand or be packedwitha quantityof -unbon'ded; relatively coarse gra l1 r'r efractory 87,such as sand o ffa' size that will not To this end; as shewn in Fig. 7,the" outerporti'on- 83 of each've'nt ma ingwbmar metar areicieqmprist ghollow; s bs'ta tiall-y cylindrical ni tal n1olrl having a "plurality ofvent" 1'2 pass through a /8" niesli screen. In order to hold the packingin place, a cup-shaped metal core box vent 88-, having a plurality ofperforations 89 inthe bottom there of, may be fixed in' the outer end ofthe vent hole, asby peenin'g'. The mold' lining is then formed in thesame manner as above" described. With this arrangement, the gasesgenerated in the lining during casting can freely escape through theporous refractory mass 87 and the perforations 89 of the core box vent88 while the latter effectively prevents the refractory packing frombeing thrown out of the vent hole under centrifugal force. It will beunderstood that; in this modification, thepaek ing 87 and core boxvent88 are relatively permanent parts of the mold, it being unnecessary torenew the'packing for each cast, but only at such times as it is desiredto thoroughly clean the vents. e I

There is thus provided by the present invention anew and improvedapparatus for centrifugally casting hollow metal articles of cast iron,steel or non-ferrous metals which is particularly well adapted totheproduction of pipe, especially pipes having-belled or flanged ends. Theapparatus lends itselfwellto rapid and efiicient production of castingswith a minimum of equipment and manual labor, and produces high quality,clean castings toclos'e tolerances and of any reasonable shape and size.

While the castings made in accordance with the pres entprocedurehaveall'of the advantageous characteristics of those made inconventional sand molds, including an u'nchilled, close grain structurefree from inclusions, the method of centrifugally lining metal moldswith a rela tively resinbonded refractory coating avoids suchdisadvantages of the prior Sandspun procedure as the" necessity formanually ramming a relatively thick green s'an'd' lining around apatternwith the aid of expensive machinery, the use of a large amount ofsand andsand handling equipment, and the need for expensive cuttingmechanism or other. means for removing the sand lining from between theflask and'the casting before the lattejtl canbe stripped from thernold.The faster freezing of the 'cast me'tal'with the relatively thinner moldlining pro vided by thepresentinvention, as well as the fact that therelatively lighterweight of the molds enables quicker acceleration oftheir rotation during the casting step, IeL-" suit in an increasedproduction rate in comparison with the sand mold process of the priorart. The procedure herein disclosed likewise embodies most of'theadvantages of the old De Iiavaud method employing metal molds, butwithout such disadvantages thereof as the excessive wear andcracking ofthe molds due to contact with themolter'f metal, and the necessity forannealing the chilled c'ast ings producedby' said method." 7

The invention also provides an improvedforrn'of' refractory lined,vented met'almold for centrifugal which'is characterized by such novelfeatures as a'rela' tivehfthin, smooth, hard, self-sustaining resinbonded refractory lining, interchangeable metal inserts for shap fingirregular ends on pipes, and anovelfornrof vent; forpermittingescape" of the gases 'whi'ch'are generated duringthe-castingoperat on: Each of 'these features con;tributestothemoreeconornical production of high grade" castings-which isthe ultimate re'sult of' the invention.

Although one specific-embodiment of apparatus embodyingthein'ventionha's -been described and illustrated in the accompanyingdrawings, itwill ibe ob vioustha't the invention is not limited to theparticularapparatus shown? but that-various changes, which 'will nowsuggest them selvesto thoseskilled the art, maybe made the form, detailsof construction and arrangement of the parts without departing from theinventive concept. Reference is therefore to be had to the appendedclaims 'foradefinition of the limits of the invention.

What is fcl'aimed is i I p l-. Are'fr'actory lihed' mold for use in 'centrifugallycast holes in the wall thereof and a relatively thin, hard,selfsustaining lining of uniform thickness consisting of a bonded massof from 95.0 to 98.5% by weight of silica sand and from 1.5 to 5.0% byweight of a fusible phenolic resin, said lining being adherent to themold wall but adapted to disintegrate as a result of burning of theresin under the heat of the cast metal and having a relatively smoothinner surface against which the metal is to be cast, the thickness ofsaid lining being a minor fraction of the thickness of the casting to beproduced but sufficient to prevent rapid freezing of the metal castagainst said surface.

2. A refractory lined mold for use in centrifugally casting tubularmetal articles comprising a hollow, substantially cylindrical metal moldhaving a plurality of vent holes in the wall thereof and a relativelythin, continuous resin bonded sand lining of uniform thickness adherentto the mold wall and covering the inner surface thereof, including theinner ends of said vent holes, said lining having a relatively smoothinner surface against which the metal is to be cast and a thicknesssubstantially less than that of the mold wall but sufficient in relationto the thickness of the casting to be produced to prevent rapid freezingof the metal cast against said surface, the character and amount of theresin in said lining being such that substantially all of said resinburns under the heat of the cast metal and thereby destroys the bondbetween the sand granules of the lining, said vent holes being adaptedto permit the escape therethrough of the gases generated in said liningduring casting.

3. A refractory lined mold as defined in claim 2 wherein the inner endof each of said vent holes has a gas permeable filling of resin bondedsand.

4. A refractory lined mold for use in centrifugally casting tubularmetal articles comprising a hollow, substantially cylindrical metal moldhaving a plurality of vent holes in the wall thereof, a relatively thin,smooth, continuous, resin bonded granular refractory lining adherent tothe mold wall and covering the inner ends of said vent holes, the resinin said lining being of such a character as to burn under the heat ofthe cast metal and thereby destroy the bond between the refractorygranules of the lining, the gases generated in said lining duringcasting escaping through said vent holes, each of said vent holes havinga relatively short inner portion of a diameter not more than about /s"and an outer portion of substantially greater diameter than said innerportion, the inner portion having a gas permeable filling of resinbonded granular refractory.

5. A refractory lined mold for use in centirfugally casting tubularmetal articles comprising a hollow, substantially cylindrical metal moldhaving a plurality of vent holes in the wall thereof, a relatively thin,smooth, continuous, resin bonded granular refractory lining adherent tothe mold Wall and covering the inner ends of said vent holes, the resinin said lining being of such a character as to burn under the heat ofthe cast metal and thereby destroy the bond between the refractorygranules of the lining, the gases generated in said lining duringcasting escaping through said vent holes, each of said vent holes havinga relatively short inner portion of less diameter than its outerportion, the outer portion being packed with a relatively coarse,unbonded granular refractory, and means for preventing the escape ofsaid packing through the outer ends of said vent holes.

6. A refractory lined mold for use in centrifugally casting tubularmetal articles comprising a hollow, substantially cylindrical metal moldhaving a plurality of vent holes in the wall thereof, each of said ventholes having a relatively short inner portion of less diameter than itsouter portion and having the outer portion packed with a relativelycoarse granular refractory of such grain size as to prevent entrythereof into the inner portion, a perforated core box vent fixed in theouter end of each of said vent holes, and a relatively thin, smooth,continuous, resin bonded granular refractory lining adherent to the moldwall and closing the inner ends of said vent holes, the resin in saidlining being of such a character as to burn under the heat of the castmetal and thereby destroy the bond between the refractory granules ofthe lining, the gases generated in said lining during casting escapingthrough said vent holes.

References Cited in the file of this patent UNITED STATES PATENTS204,479 Burns June 4, 1878 263,448 Withey Aug. 29, 1882 359,483 WhitleyMar. 15, 1887 428,422 Skinner May 20, 1890 1,559,779 Rice Nov. 3, 19251,675,716 Losey July 3, 1928 2,399,606 Schuh et a1 Apr. 30, 19462,623,809 Myers Dec. 30, 1952 FOREIGN PATENTS 660,693 Great Britain Nov.14, 1951 OTHER REFERENCES The Foundry, October 1950, pages 162, 164 and168. FIAT Final Report 1168, 6 pages.

